The present invention relates to photographic cameras and, in particular, to photographic cameras having flash illumination systems.
Conventional cameras capture images on a photosensitive element by exposing the photosensitive element to light from a scene. Such a photosensitive element is typically capable of recording useful images when exposed to light within a predetermined range. Thus, conventional cameras carefully meter exposures so that the light from the scene that strikes the photosensitive element is within the predefined range.
Exposure metering is typically controlled by a shutter mechanism. The shutter mechanism exposes the photosensitive element to light from the scene for a period of time known as an exposure time. The exposure time needed for a useful image to form on the photosensitive element is generally inversely proportional to the amount of light in the scene. Accordingly, many cameras feature an exposure control system that monitors photographic conditions such as the ambient light in a scene and that causes the shutter mechanism to modify the exposure time in proportion to the amount of light in the scene. This optimizes the appearance of the image captured on the photographic element. Often cameras incorporate flash systems that emit a flash of light to provide supplemental illumination of the scene. The exposure control systems of certain flash cameras adapt the operation of the shutter mechanism to modify the exposure accordingly.
It will be appreciated that such adaptive exposure control systems are complex and, accordingly, they can be challenging to design, manufacture and install in a camera. Thus, such exposure control systems are typically incorporated in more expensive point and shoot and single lens reflex cameras.
A lower cost exposure control approach is to provide a camera that has a fixed exposure time that is calibrated so that the camera is likely to capture an acceptable image under a wide range of conditions including ambient light images and flash images. However, a disadvantage of this solution is that such cameras are not fully optimized to capture images at the extremes of these ranges.
An example of such a camera is shown in JP 8-278, 529A which shows a camera with an exposure control system having a movable shutter and a camera body having various positions for receiving a stop that limits the path movement of the shutter blade during exposure. During camera manufacture, the stop is located at one of the positions. When the camera is recycled, the manufacturer can move the stop to shorten or extend the path of travel of the shutter. By shortening or extending the path of travel of the shutter, the exposure time is shortened or lengthened so that the same camera body can be used to accommodate the exposure needs of different film, flash, or lens arrangements. However, it is important to note that the location of the stop and therefore the exposure time is fixed until the next time the camera is recycled.
Thus what is needed is a low cost camera exposure control system that adapts the exposure to optimize the appearance of captured images.
One attempt to meet this need is JP 08-211,447 which shows a shutter mechanism that has a shutter that has a path of travel that is limited by a halt member. The halt member is movable to permit adjustment of the exposure. An opening in the cover permits a user to manually move the halt member. The biasing spring that propels the shutter is also connected to the halt member. As the halt member is moved, the amount of bias applied to the shutter changes. This changes the speed at which the shutter is moved during an exposure. This system requires that the user of the camera must make the determination as to which speed settings are appropriate for a particular photographic circumstance. However, this determination can be difficult for even advanced amateurs to make.
This determination becomes even more difficult to make when such a speed control is implemented in a camera that also incorporates a flash system the user can selectively enable and disable. This is because the presence or absence of flash illumination in a scene can significantly influence whether a particular speed setting is appropriate. Cameras having such user enabled flash systems are well known. One example of a camera having such a user enabled flash is shown in JP 11-282,060A. In this camera a flash illumination circuit is provided that discharges a flash of light when a switch is closed. The switch is a two contact switch that is controllably disabled by a user controlled insulator that is positioned between the two contacts. This prevents the contacts from engaging and disables the flash. In JP 11-282,060 A, a similar system is used. However in this system, the contacts are bent apart from each other to prevent them from engaging as the shutter blade makes contact with the switch. JIP 11-64940 shows a flash illumination circuit having a switch with an on and off position wherein the illumination charge and discharge circuits are disabled by the switch. . This circuit requires that the flash illumination circuit is electrically adapted to accommodate this disabling switch. While such cameras provide the ability to selectably enable and disable the flash, they do not optimize exposure conditions to reflect the condition of the flash.
What is needed therefore is a low cost camera and camera exposure control system having a flash illumination system that can be enabled and disabled by a user and that automatically adjusts exposure characteristics to optimize the appearance of images captured in either flash or ambient light photography modes.
In a first aspect of the present invention, a camera exposure control system is provided. The camera exposure control system has a shutter movable during an exposure period through a path of travel between a first position and a second position and a detector to sense the shutter and to generate a signal when the shutter is at a flash trigger position in the path of travel. A flash circuit is provided and receives the signal generated by the detector causing a flash of light to discharge when the signal is received. A stop is also provided. The stop is selectably movable from a location out of the path of travel of the shutter to a location in the path of travel of the shutter. The location of the stop determines whether the detector can sense the shutter during the exposure.
In another aspect of the present invention, a camera is provided having a housing with an opening to admit light from a scene. An imaging gate is provided and positions an imaging surface to receive the light from the scene. A shutter is provided and is movable during an exposure period through a path of travel between a first position wherein the shutter blocks light from the scene from traveling to the imaging surface and a second position wherein the shutter permits light from the scene to travel to the imaging surface. A detector sense the shutter and generates a signal when the shutter is at a flash trigger position in the path of travel. A flash circuit receives the signal generated by the detector and causes a flash of light to discharge when the shutter electrically engages the contact. A stop is provided and is selectably movable from a location out of the path of travel of the shutter to a location in the path of travel of the shutter. The location of the stop determines whether the shutter can engage the contact during the exposure.